Messages in this thread | | | From | Arnd Bergmann <> | Date | Sat, 13 Feb 2021 00:05:43 +0100 | Subject | Re: [RFC] IRQ handlers run with some high-priority interrupts(not NMI) enabled on some platform |
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On Sat, Feb 13, 2021 at 12:00 AM Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com> wrote: > > -----Original Message----- > > From: Arnd Bergmann [mailto:arnd@kernel.org] > > Sent: Saturday, February 13, 2021 11:34 AM > > To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com> > > Cc: tglx@linutronix.de; gregkh@linuxfoundation.org; arnd@arndb.de; > > geert@linux-m68k.org; funaho@jurai.org; philb@gnu.org; corbet@lwn.net; > > mingo@redhat.com; linux-m68k@lists.linux-m68k.org; > > fthain@telegraphics.com.au; linux-kernel@vger.kernel.org > > Subject: Re: [RFC] IRQ handlers run with some high-priority interrupts(not NMI) > > enabled on some platform > > > > On Fri, Feb 12, 2021 at 2:18 AM Song Bao Hua (Barry Song) > > <song.bao.hua@hisilicon.com> wrote: > > > > > So I am requesting comments on: > > > 1. are we expecting all interrupts except NMI to be disabled in irq handler, > > > or do we actually allow some high-priority interrupts between low and NMI > > to > > > come in some platforms? > > > > I tried to come to an answer but this does not seem particularly well-defined. > > There are a few things I noticed: > > > > - going through the local_irq_save()/restore() implementations on all > > architectures, I did not find any other ones besides m68k that leave > > high-priority interrupts enabled. I did see that at least alpha and openrisc > > are designed to support that in hardware, but the code just leaves the > > interrupts disabled. > > The case is a little different. Explicit local_irq_save() does disable all > high priority interrupts on m68k. The only difference is arch_irqs_disabled() > of m68k will return true while low-priority interrupts are masked and high > -priority are still open. M68k's hardIRQ also runs in this context with high > priority interrupts enabled.
My point was that on most other architectures, local_irq_save()/restore() always disables/enables all interrupts, while on m68k it restores the specific level they were on before. On alpha, it does the same as on m68k, but then the top-level interrupt handler just disables them all before calling into any other code.
It's possible that I missed some other implementation doing the same as m68k, as this code is fairly subtle on some architectures.
Arnd
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